The increased integration of transistors on single chips made possible by the submicron CMOS technology raises the problem of speed and performance limitation of electronic systems through the interconnect structures between chips or with other structures. A possible solution to this problem of CMOS interconnect bottlenecks could be the use of optical links or interconnects between chips. In a number of applications, especially to achieve high density interconnects, optical interconnects are advantageous over electrical interconnects. For instance, optical interconnects can reach a higher interconnect density and lower power consumption than electrical interconnects.
In order to achieve high density optical interconnects, it is necessary to realize high density arrays of light sources and light detectors, and furthermore to use an optical path or channel between sources and detectors which sustains a high density of optical channels. The light sources used to send the optical signals through the optical interconnect channels receive their input and possibly at least part of their power from electrical signals. These electrical signals can originate from an integrated circuit, or from a board. Furthermore, at the other end of the optical interconnect channel are detectors, which also require electrical power to operate, and which convert the received optical signals into electrical signals. Hence, it is clear that high density optical interconnects require a high density of electrical or optical devices to possibly deliver at least part of the required electrical power to run the optical interconnect, as well as to send and retrieve the signals.
Obviously, the foregoing analysis can be applied as well to interconnect systems that make use of another form of electromagnetic radiation than light.
In many optical applications, it is required to have a transparent substrate for an optoelectronic device such as a light-emitting device, a photodetector, a modulator or a CCD sensor. An application example is when an optoelectronic device is contacted from the front side by flip-chip mounting, while the light has to be transported through the substrate. Many substrates are poorly or not transparent for the light emitted or detected in the active semiconductor layers grown on them. For example, Gallium-Arsenide (GaAs) or Aluminium-Gallium-Arsenide (AlGaAs) or InGaP or InAlGaP active layers emit and detect light with a peak wavelength that is strongly absorbed by the GaAs substrate on which they are typically grown. Hence, light-emission or light-detection through the original substrate is not possible. A possible solution to this problem is to remove the original substrate in a process such as described in U.S. Pat. No. 5,578,162. Another possible solution is to replace the original substrate by a transparent substrate, such as a glass plate.
U.S. Pat. No. 5,093,879 discloses an optoelectrical connector for accommodating high density applications. This patent specification however does not disclose and does not enable to fabricate integration neither alignment of a connection for the electrical signals to the devices for emitting and/or detecting electromagnetic radiation, wherein the functioning of said devices is being controlled by said electrical signals.
U.S. Pat. No. 5,625,811 discloses an optically interconnected multichip module. The patent shows a dense integration of thin layers of semiconductor material with devices (chips) integrated therein and which are bonded to a fiber optic face plate. These chips are integrated in a multichip module and the fiber optic face plate is providing the optical intraconnection or optical transmission medium between the chips. The optical intraconnection (waveguide) is not flexible and does not allow for communication between chips which are in the same plane or in a remote location. This patent does not address the problem of a connector to an external apparatus or external devices that is versatile in use and easy to use.
The use of fiber optic face plates in combination with optoelectrical devices has further been proposed, e.g. in U.S. Pat. No. 5,074,683, and in U.S. Pat. No. 5,652,811, and in U.S. Pat. No. 5,578,162.
U.S. Pat. No. 5,631,988 discloses an optical interconnect that couples multiple optical fibers to an array of optoelectrical devices. The connector comprises a holder, a plurality of optical fibers attached to the holder, and guiding means. This connector is quite elaborate and not compaction in providing the optical path of the interconnection signals. Moreover, the direct contact of the optical fiber bundles to the optoelectrical devices can degrade such devices, in particular because the optical connection is detachable.
U.S. Pat. No. 5,367,593 provides an optical/electrical connector that includes a molded base with alignment guides and with a well for integrating an electronic circuit. Also this device is not compact and provides an optical interconnection path only for a 1-dimensional array. The teaching of this patent does not disclose nor does it suggest an optoelectrical interconnect in a dense and compact configuration which is flexible in use for a multitude of configurations such as 2-dimensional arrays of light-emitting devices on an electronic circuit.